This invention relates generally to a system for pneumatically conveying a batch of fluent particulate material from one holding tank or storage vessel to another. More particularly, this invention relates to a machine having a bulk material loading container in which an air permeable particle filter is disposed through which a vacuum is drawn on the container so as to induce a flow of such material therein from a remote source after which, the vacuum is interrupted and the container is exposed to atmospheric pressure for backflushing the filter and for discharging material from the container.
Generally speaking, such systems are known in the prior art. See U.S. Pat. No. 3,169,038 issued to F. P. Pendleton on Feb. 9, 1965 and U.S. Pat. No. 4,372,713 issued to James P. Kean, Jr. on Feb. 8, 1983.
The patent to Pendleton discloses what could be considered a loading container having such a filter disposed in an upper portion thereof. Compressed air is passed through the throat of a venturi tube, which tube communicates with the interior of the container through the filter so as to produce a partial vacuum therein for inducing the flow of bulk material into the container from a remote source. After the desired amount of material has been induced into the container, an inlet port through which the material flows is closed shutting off the further flow of material but compressed air continues to flow through the venturi for a time to increase the vacuum drawn on the container through the filter. After the desired high vacuum has been created, compressed air is removed from the venturi so that a heavy volume of atmospheric air rushes into the throat of the venturi and thence through the filter and into the container, whereby the filter is flexed by a rapid snapping action to shake off any coating of material that may be adhered to its outer surface.
The patent to Kean, Jr. discloses a bulk material loading container which contains what could be described as a two stage air permeable particle filter operated by a pair of air diverter valves. A vacuum pump is connectable to either or both filter stages and can be isolated from either or both stages depending upon the settings of the two diverter valves. Prior to the container filling operation, one diverter valve is set so as to permit ambient air to flow into the container through the first filter stage to backflush and clean the latter while the other valve is set so as to connect the pump to the second stage to draw the ambient air introduced into the container through first stage out of the container. After a time, the first mentioned diverter valve operates to isolate the first stage from ambient atmosphere and connect that stage to the vacuum pump such that a partial vacuum will then be drawn on the container through both stages to induce material to flow into the container from a remote source. After the container filling operation is completed, the second valve operates to isolate the second stage from the pump and expose that stage to ambient atmosphere, whereby the second stage is backflushed. During second stage backflushing, ambient air thus introduced into the container is withdrawn by the pump which is still connected to the first stage. Upon completion of the second stage backflushing operation, the first diverter valve again switches to also expose the first stage to ambient atmosphere at which time a counterweighted door, pivotally connected to the base of the container for sealing a discharge orifice, tilts open under the weight of material in the container to allow the accumulated material to be discharged.
The Pendleton device is complicated by the use of an air compressor in combination with a venturi to generate two different vacuum levels in the container during two successive time periods, the first being a low vacuum level for filling the container and the second being a high vacuum level necessary to cause sufficient inrush of ambient air through the filter upon removal of the second level to adequately backflush and clean the filter.
The Kean, Jr. device is complex in that it employs a two stage filter operated by a pair of air diverter valves which must execute four separate and distinct steps during each cycle of operation of the system. An additional difficulty encountered with the Kean, Jr. device is that material can not be discharged from the container during a filter backflushing operation.
By means of our invention, these and other difficulties encountered with prior art bulk material conveying systems are substantially overcome.